When I play the fourth note of a sequence, it fails and produces a sound like a pop. To be more clear I add some details:- the problem is still present playing the same note for four times consecutively: for the first three times all is ok..but the fourth it fails;- the problem is present also in polyphonic playing: for example holding down two keys, if I press another key it sounds good, but the note that I'll play after that will produce the unwanted pop - the problem is present both with preset and panel mode, even if in the second case, arranging some parameters the problem can be masked a little

Since the CS-50 is a 4 poly synth, could be a problem of the buffer? And in this case which one?

Thank you for your answer pflosi but I'm a real noob ...and maybe I can't understand what does it mean.Was my guess right? For example could it be a problem of the 4th s/h circuit?Or the voice 4 problem, the one you are referring to, is related to one of the several blocks along the voice4 line?

As I understand it, there are four voice cards inside the machine (1 for each voice). Your problem is probably with the fourth one. I beleive the voices all come before the filters and all that other stuff.

Mine has an intermittent problem with voice #4 as well. It does not pop but the notes are off. (Well, every 4th note is off, anyway.).

The thing about mine is that it only happens sometimes and then it goes away.

I think your best option is to take it to a tech and have them look at it.

Normally, the problem shows up after the synth has warmed up for a while (if it shows up at all). Today that's exactly what happend but I tried somethign I have never done in the nearly 20 years I have owned it. I left it on for a couple of hours. When I came back to it the problem was totally gone and the tuning is perfect from voice to voice.

I am taking it to be serviced tomorrow. I sure hope they can diagnose the problem if it doesn't show up.

If you're lucky, it's a dodgy capacitor on the voice 4 board. If you're not lucky, it's one of the chips, they're CMOS and are at the end of their lifespan pretty much.

If you don't know much about electronics, servicing this instrument is not a good way to learn.

You can eliminate the "buffer" (as you call it) as an issue if you swap the boards around. Put the "faulty" board in slot 3. If the fault happens on every third note, then you know it's the voice board and not the keyboard control circuitry.